4 * Wireshark - Network traffic analyzer
5 * By Gerald Combs <gerald@wireshark.org>
6 * Copyright 1998 Gerald Combs
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version 2
11 * of the License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
24 #ifndef __WSUTIL_BITS_COUNT_ONES_H__
25 #define __WSUTIL_BITS_COUNT_ONES_H__
32 * The variable-precision SWAR algorithm is an interesting way to count
33 * the number of bits set in an integer. While its performance is very
34 * good (two times faster than gcc's __builtin_popcount [1] and
35 * 16 instructions when compiled with gcc -O3)
36 * http://playingwithpointers.com/swar.html
40 ws_count_ones(const guint32 x)
44 bits = bits - ((bits >> 1) & 0x55555555);
45 bits = (bits & 0x33333333) + ((bits >> 2) & 0x33333333);
46 bits = (bits + (bits >> 4)) & 0x0F0F0F0F;
48 return (bits * 0x01010101) >> 24;
51 #endif /* __WSUTIL_BITS_COUNT_ONES_H__ */